Disclosed herein is a process for producing an imaging member belt having a butt-lap seam design. This disclosure also provides a flexible imaging member belt having a number of morphological improvements and, more specifically, to the creation of a thin and smooth profile seam for flexible electrostatographic imaging member belts.
Flexible electrostatographic belt imaging members are well known. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems, electroreceptors such as ionographic imaging members for electrographic imaging systems, and intermediate image transfer belts for transferring toner images in electrophotographic and electrographic imaging systems. These belts are usually formed by cutting a rectangular, a square, or a parallelogram shape sheet from a web containing at least one layer of thermoplastic polymeric material, overlapping opposite ends of the sheet, and joining the overlapped ends together to form a seam. The seam typically extends from one edge of the belt to the opposite edge.
Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The “imaging layer” as employed herein is defined as the dielectric imaging layer of an electroreceptor belt, the transfer layer of an intermediate transfer belt and, the charge transport layer of an electrophotographic belt. Thus, the thermoplastic polymeric matrix material in the imaging layer is located in the upper portion of a cross section of an electrostatographic imaging member belt, the substrate layer being in the lower portion of the cross section of the electrostatographic imaging member belt. Although the flexible belts of interest include the mentioned types, for simplicity reasons, the discussion hereinafter will be focus on the electrophotographic imaging member belts.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the entire disclosure thereof being incorporated herein by reference. The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers have been developed, fatigue induced cracking of the charge transport layer at the welded seam area is frequently encountered during photoreceptor belt cycling. Moreover, the onset of seam cracking has also been found to rapidly lead to seam delamination due to fatigue thereby shortening belt service life.
The flexible electrostatographic imaging member belts are fabricated from a sheet cut from an imaging member web. The sheets are generally rectangular or parallelogram in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the preferred method of joining because it is rapid, clean (no solvents) and produces a thin and narrow seam. In addition, ultrasonic welding is preferred because the mechanical pounding of the welding horn causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers therein. A typical ultrasonic welding process is carried out by holding down the overlapped ends of a flexible imaging member sheet with vacuum against a flat anvil surface and guiding the flat end of an ultrasonic vibrating horn transversely across the width of the sheet, over and along the length of the overlapped ends, to form a welded seam.
When ultrasonically welded into a belt, the seam of multilayered electrophotographic imaging flexible member belts may occasionally contain undesirable high protrusions such as peaks, ridges, spikes, and mounds. These seam protrusions present problems during image cycling of the belt machine because they interact with cleaning blades to cause blade wear and tear which ultimately affect cleaning blade efficiency and service life. Moreover, the protrusion high spots in the seam may also interfere with the operation of subsystems of copiers, printers and duplicators by damaging electrode wires used in development subsystems that position the wires parallel to and closely spaced from the outer imaging surface of belt photoreceptors. These closely spaced wires are employed to facilitate the formation of a toner powder cloud at a development zone adjacent to a toner donor roll and the imaging surface of the belt imaging member.
Another frequently observed mechanical failure in the imaging belts during image cycling is that the ultrasonically welded seam of an electrophotographic imaging member belt can also cause initiation of cracks in the seam which then propagate and lead to delamination after being subjected to extended bending and flexing cycles over small diameter belt support rollers of an imaging machine or when due to lateral forces caused by mechanical rubbing contact against stationary web edge guides of a belt support module during cycling. Seam cracking and delamination has also been found to be further aggravated when the belt is employed in electrophotographic imaging systems utilizing blade cleaning devices and some operational imaging subsystems. Alteration of materials in the various photoreceptor belt layers such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or charge transport layer to suppress cracking and delamination problems is not easily accomplished. The alteration of the materials may adversely impact the overall physical, electrical, mechanical, and other properties of the belt such as well as coating layer uniformity, residual voltage, background, dark decay, flexibility, and the like.
For example, when a flexible imaging member belt used in an electrophotographic machine is a photoreceptor belt fabricated by ultrasonic welding of overlapped opposite ends of a sheet, the ultrasonic energy transmitted to the overlapped ends melts the thermoplastic sheet components in the overlap region to form a seam. The ultrasonic welded seam of a multilayered photoreceptor belt is relatively brittle and low in strength and toughness. The joining techniques, particularly the welding process, can result in the formation of a splashing that projects out from either side of the seam in the overlap region of the belt. The overlap region and splashings on each side of the overlap region comprise a strip from one edge of the belt to the other that is referred herein as the “seam region”. The seam region of a typical overlap seamed flexible belt is about 1.6 times thicker than the thickness of the body of the belt. Because of the splashing, a typical flexible imaging member seamed belt has sharp top splashing height of about 76 micrometers above the surface of the imaging layer at the junction meeting point between the top splashing and the surface of the belt. The junction meeting point is the undesirable site of physical discontinuity which has been found to act as stress concentration point to facilitate early onset of seam cracking/delamination problems under dynamic fatigue imaging member belt machine functioning conditions.
The photoreceptor belt in an electrophotographic imaging apparatus undergoes bending strain as the belt is cycled over a plurality of support and drive rollers. The excessive thickness of the photoreceptor belt in the seam region due to the presence of the splashing results in a large induced bending strain as the seam travels over each roller. Generally, small diameter support rollers are highly desirable for simple, reliable copy paper stripping systems in electrophotographic imaging apparatus utilizing a photoreceptor belt system operating in a very confined space. Unfortunately, small diameter rollers, e.g., less than about 0.75 inch (19 millimeters) in diameter, raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt seam failure can become unacceptable for multilayered belt photoreceptors. For example, when bending over a 19 millimeter diameter roller, a typical photoreceptor belt seam splashing may develop a 0.96 percent tensile strain due to bending. This is 1.63 times greater than a 0.59 percent induced bending strain that develops within the rest of the photoreceptor belt. Therefore, the 0.96 percent tensile strain in the seam splashing region of the belt represents a 63 percent increase in stress placed upon the seam splashing region of the belt.
Under dynamic fatiguing conditions, the seam provides a focal point for stress concentration and becomes the point of crack initiation which is further developed into seam delamination causing premature mechanical failure in the belt. Thus, the splashing tends to shorten the mechanical life of the seam and service life of the flexible member belts used in copiers, duplicators, and printers. Moreover, the known seam splashing surface roughness has also been found to interfere with cleaning blade function resulting in premature blade wear problem causing its loss of cleaning efficiency.
Although a solution to suppress the seam cracking/delamination problems has been successfully demonstrated, as described in a prior art, by a specific heat treatment process of a flexible electrophotographic imaging member belt with its seam parked directly on top of a 19 mm diameter back support rod for stress-releasing treatment at a temperature slightly above the glass transition temperature (Tg) of the charge transport layer of the imaging member, nevertheless this seam stress release process was also found to produce various undesirable effects such as causing seam area imaging member set and development of belt ripples in the active electrophotographic imaging zones of the belt (e.g., the region beyond about 25.2 millimeters from either side from the midpoint of the seam). Moreover, the heat treatment can induce undesirable circumferential shrinkage of the imaging belt. The set in the seam area of an imaging member mechanically adversely interacts with the cleaning blade and impacts cleaning efficiency. The ripples in the imaging member belt manifest themselves as copy printout defects. Further, the heat induced imaging belt dimensional shrinkage alters the precise dimensional specifications required for the belt. Another key shortcoming associated with the prior art seam stress release heat treatment process is the extensive heat exposure of a large seam area. This extensive heat exposure heats both the seam area of the belt as well as the rod supporting the seam. Since the belt must be cooled to below the glass transition temperature of the thermoplastic material in the belt prior to removal from the support rod in order to produce the desired degree of seam stress release in each belt, the heat treatment and cooling cycle time is unduly long and leads to very high belt production costs. Furthermore, it has been found that seam cracking life extension can be achieved through seam stress processing, nevertheless the surface roughness produced by seam splashing still produces difficulties with respect to the cleaning blade function.
Since there is no effective way to prevent the generation of localized high protrusion spots at the seam region, imaging member belts are inspected right after seam welding belt production process, manually by hand wearing a cotton glove through passing the index finger over the entire seam length. Belts found catching the glove by the protrusion spots are identified as production rejects. Both the time consuming procedure of manual inspection and the number of seamed belts rejected due to the presence of high seam protrusion spots constitute a substantial financial burden on the production cost of imaging member belts.
Therefore, there is a need to provide seamed flexible imaging belts with an improved seam morphology which can withstand greater dynamic fatigue conditions thereby extending belt service life. It is also important, from a production point of view, to reduce the unit manufacturing cost of seamed imaging belts. This can be realized, in part, if a seam design can be developed to provide a smooth surface free of protrusion spots, reduce seam thickness, with little or no splashing to eliminate or minimize physical discontinuity at the junction or mating point of the seam.
The following references may be relevant to certain aspects of this disclosure:
U.S. Pat. No. 5,688,355 to Yu, issued Nov. 18, 1997—A seamed flexible belt and process for fabricating the belt is disclosed. Multiple-layered electrophotographic imaging member belt is prepared by utilizing excimer laser ablation technique to remove precision amount of material from the bottom and the top of two opposite ends of an imaging member cut sheet prior to overlapping the two opposite ends and ultrasonically weld the overlap into a welded seam. The resulting multi-layered imaging member belt thus obtained has a welded seam of little added thickness and reduced amount of seam splashing formulation.
U.S. Pat. No. 5,698,358 to Yu, issued Dec. 16, 1997—Disclosed is a process including providing a flexible substantially rectangular sheet having a first major exterior surface opposite and parallel to a second major exterior surface, removing or displacing material from the first exterior surface adjacent and parallel to a first edge of the sheet to form a new surface having an elongated, curvilinear “S” shaped profile when viewed in a direction parallel to the first edge, overlapping the new first surface and a second surface adjacent a second edge of the sheet whereby the first new surface contacts the second surface to form a mated surface region, the second surface being adjacent to or part of the second major exterior surface to form a sheet into a loop, the second edge being at an end of the sheet opposite from the first edge, and permanently joining the new first surface to the second surface into a seam to form a seamed belt. The resulting welded belt has a seam thickness of less than about 120 percent of the total thickness of the belt.
U.S. Pat. No. 5,190,608 to Darcy et al., issued Mar. 2, 1993—A flexible belt is disclosed having an outwardly facing surface, a welded seam having irregular protrusion on the outwardly facing surface and a thin flexible strip laminated and covering the welded seam and protrusions. This belt may be fabricated by providing a flexible belt having an outwardly facing surface and a welded seam having irregular protrusions on the outwardly facing surface and laminating a thin flexible strip to the welded seam. The belt may be used in an electrostatographic imaging process.
U.S. Pat. No. 5,549,999 to Swain et al., issued Aug. 27, 1996 —Disclosed is a process for coating flexible belt seams including providing a flexible belt having an outwardly facing surface and a welded seam, forming a smooth liquid coating comprising a hardenable film forming polymer on the welded seam, the coating being substantially free of fugitive solvent, and hardening the coating to form a smooth solid coating on the seam.
U.S. Pat. No. 5,582,949 to Bigelow et al., issued Dec. 10, 1996—A process for coating flexible belt seams is disclosed wherein the process includes providing a flexible belt having an outwardly facing surface and a welded seam, forming a smooth liquid coating on the welded seam, the liquid coating comprising a film forming polymer and a fugitive liquid carrier in which the belt surface is substantially insoluble, and removing the fugitive liquid carrier to form a smooth solid coating on the seam.
U.S. Pat. No. 6,328,922 B1 to Mishra et al., issued Dec. 11, 2001—A process for the post treatment of an imaging member belt including providing a support member having a smooth flat surface, proving a flexible belt having a welded seam, supporting the inner surface of the seam on the smooth flat surface, contacting the seam with a heated surface, heating the seam region with the heated surface to raise the temperature in the seam region to a temperature of from about 2° C. to 20° C. about the Tg of the thermoplastic polymer material, and compressing the seam with the heated surface with sufficient compression pressure to smooth out the seam is disclosed herein.
U.S. Pat. No. 5,552,005 to Mammino et al., issued Sep. 3, 1996 —A flexible imaging sheet and a method of constructing a flexible imaging sheet is disclosed. The method of constructing a flexible imaging sheet comprises the steps of overlapping, joining, and shaping. In the step of overlapping, a first marginal end region and a second marginal end region of a sheet are overlapped to form an overlap region and a non-overlap region. In the step of joining, the first marginal end region and the second marginal end region of the sheet are joined to one another by a seam in the overlap region. In the step of shaping, the overlap region is shaped to form a generally planar surface co-planar with a surface of the non-overlap region. The flexible imaging sheet comprises a first marginal end region and a second marginal end region. The first marginal end region and the second marginal end region are secured by a seam to one another in the overlap region. The first marginal end region and the second marginal end region are substantially co-planar to minimize stress on the flexible imaging sheet. Minimization of stress concentration, resulting from dynamic bending of the flexible imaging sheet during cycling over a roller within an electrophotographic imaging apparatus, is disclosed therein.
U.S. Pat. No. 6,074,504 to Yu et al., issued Jun. 13, 2000—A process is disclosed for treating a seamed flexible electrostatographic imaging belt including providing an imaging belt having two parallel edges, the belt comprising at least one layer comprising a thermoplastic polymer matrix and a seam extending from one edge of the belt to the other, the seam having an imaginary centerline, providing an elongated support member having at arcuate supporting surface and mass, the arcuate surface having at least a substantially semicircular cross section having a radius of curvature of between about 9.5 millimeters and about 50 millimeters, supporting the seam on the arcuate surface with the region of the belt adjacent each side of the seam conforming to the arcuate supporting surface of the support member, precisely traversing the length of the seam from one edge of the belt to the other with thermal energy radiation having a narrow Gaussian wavelength distribution of between about 10.4 micrometers and about 11.2 micrometers emitted from a carbon dioxide laser, the thermal energy radiation forming a spot straddling the seam during traverse, the spot having a width of between about 3 millimeters and about 25 millimeters measured in a direction perpendicular to the imaginary centerline of the seam, and rapidly quenching the seam by thermal conduction of heat from the seam to the mass of the support member to a temperature below the glass transition temperature of the polymer matrix while the region of the belt adjacent each side of the seam conforms to the arcuate supporting surface of the support member.
While various innovative approaches have provided improvements in flexible belt seam morphology, nevertheless, it has been found that the solution of one problem may also create other undesirable issues. For example, overcoating the seam of a photoreceptor belt with metallic foil could cause electrical seam arcing. Moreover, application of liquid overcoating layer over the seam also induces the crystallization of charge transport molecules in the vicinity adjacent to the seam overcoat. Additionally, it was also observed that application of the liquid overcoating layer usually produced poor adhesion bond strength to the seam after solidification into a dried coat. Thus, there is a continuing need for electrostatographic imaging belts having improved welded seam designs that are thin in seam profile, resistant to seam cracking/delamination, free of seam protrusions, have improved seam region physical continuity, and are free of factors that damage imaging subsystems.